Aluminum connection parts treated with concentrated nitric acid



-'will reduce the contact resistance Patented Mar. 2, 1 948 2,437,220ALUMNUM CONNECTION PARTS TREATED WITH CONCENTRA TED NITRIC ACID WilhelmFriedrich Bonwitt, Mount Vernon, N. Y.,

assignor to Burndy Engineering Company,

Inc., a corporation of New York No Drawing. Application June 26, 1943,Serial No. 492,416

My invention relates to a treatment for aluminum conductor surfaces todecrease electrical contact resistance.

It is commonly known that special care has to be taken when making anelectrical connection between parts made from aluminum. The surface ofaluminum is seldom clean but mostly covered with a film of oxide, whichforms rapidly even at normal temperatures and atmospheres. This oxidefilm is an extremely poor conductor and therefore the cause of contacttroubles. An additional cause for contact difliculties is the fact thatit is hard to maintain a sufliciently high contact Pressure because ofthe softness and ductility of pure aluminum.

The primary object of my invention therefore is to provide a, treatmentfor aluminum conductors employed in electrical connections which willincrease the electrical joint efficiency as compared with untreatedconductors.

Another object is to provide a treatment which especially on crimped orindented joints.

Other objects are to provide a treatment of the foregoing character inwhich the results will be stable over long periods of time, and toprovide means for protecting the surfaces so produced.

I accomplish these and other objects and obtain my novel results as willbe apparent from the precedure described hereinafter, and particularlypointed out in the attached claims.

My invention consists in treating the contact surfaces of the aluminumparts with concentrated nitric acid for a short period of time, fiveminutes at room temperature being satisfactory. The part is then removedfrom the acid and dried. It is important that the drying be done withoutmechanically rubbing, wiping or rinsing. Blowing the excess acid of!with air and letting the part dry slowly (about one hour) was foundeffective. When the part is dry, care should be taken not to wipe orscratch the surface.

The application of a" zinc-petrolatum compound to the treated surfaceshas a two-way preserving effect. First, it protects the surface afterthe treatment whenever the connection cannot be made immediately.Second, it has a protective function after the joint is made, by actingas a seal. I have found it desirable to dry the treated surfacethoroughly before applying the zinc-petrolatum. Zincmetrolatum is amixture of metallic zinc dust suspended in heavy petrolatum jelly. Thezine dust acts as a cathodic means to inhibit corrosion on the contactsurfaces.

The treatment of only one member of a pair 3 Claims. (Cl. 174-126) incontact, has been found to establish a satisfactory lowering of thecontact resistance.

Extended tests have consistently shown that the resistance of joints towhich the treatment was applied, is not only practically unaffected bysevere aging tests but also was considerably lower than the resistanceof indented joints made with aluminum which had not been prepared beforerent therethrough said connector being made of metal contacting parts atleast one of which is aluminum, said aluminum part having a goodconducting surface thereon obtained by treating it with concentratednitric acid which is immediately air dried only.

3. A metal conductor made of aluminum having a contacting face fordirect engagement with another contacting face for transmitting currenttherethrough, said aluminum contacting face having a good conductingsurface thereon obtained by treating it with concentrated nitric acidwhich is immediately air dried only.

WILHELM FRIEDRICH BONWITT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Transactions of the Faraday Soc.,1934, pages 6

